Petroleum streams that contain metals are typically problematic in refineries as streams because the metallic components contained therein have a negative impact on certain refinery operations. Thus, demetallation has been referred to as critical to help conversion of crude fractions (see e.g., Branthaver, Western Research Institute in Ch. 12, "Influence of Metal Complexes in Fossil Fuels on Industrial Operations", Am. Chem. Soc. (1987)). Such metals, for example, act as poisons for hydroprocessing and fluid catalytic cracking catalysts, thereby, shortening the run length of such processes, increasing waste gas make and decreasing the value of coke product from coker operations.
The presence of such metals prevents more advantageous use of the petroleum stream by rendering especially the heaviest oil fractions (in which these metal containing structures most typically occur) less profitable to upgrade, and when these resources are used they make catalyst replacement/disposal expensive. Current refinery technologies typically address the problem by using metal containing feedstreams as a less preferred option, and by tolerating catalyst deactivation when there are not other feedstream alternatives available.
Electrochemical processes have been used for removal of halogenated organic compounds, e.g., polychlorinated biphenyls in one phase organic systems see e.g., U.S. Pat. No. 5,102,510 and for removal of water soluble metals from aqueous streams, see e.g., U.S. Pat. No. 3,457,152. Petroleum streams are typically not halogen containing. Removal of metals from complex petroleum streams is more difficult because the metals are associated with hydrocarbon species, and are not readily water soluble. U.S. Pat. No. 5,529,684 discloses a process for electrochemically demetallating petroleum streams, but there is a continuing need for an effective method for removal of these metals particularly ones in which enhanced rates of demetallation, at higher current efficiencies and/or lower electrolyte concentrations are possible. Applicants' invention addresses this need.